The current practice of inserting artificial heart valves involves cutting the chest open, placing the patient on cardiopulmonary bypass, and surgically inserting the valve into an aorta. This process can take several hours and subjects the patient to significant operative mortality. While the mortality during first valve replacement surgery can be very low (less than 5%), the second surgery carries much greater operative mortality, and the third is even more risky ( greater than 15%). Consequently, first and second re-operations to replace a worn out bioprosthetic heart valve are avoided. Since a typical bioprosthesis, or tissue valve, can wear out in 10 years, these valves are typically implanted into patients 60 years old, or older. Younger patients are often recommended a mechanical valve that does not wear out, and typically does not need replacement.
Tissue valves, however, are often preferred over mechanical valves because of their better biocompatibility. Mechanical valves cause blood to clot on their components, and the patient must therefore be chronically treated with anticoagulants to eliminate the risk of major blood clots. Anticoagulant themselves, however, carry a measurable risk of bleeding and thromboembolism and are not an ideal solution. Because tissue valves do not need to be anticoagulated, they are potentially the ideal valve prosthesis, if only their durability were to be improved.
Accordingly, the goal of most tissue valve research and development, has been the improvement in valve durability so that these tissue valves can be put into patients younger than 60 or 65. Because of the operative mortality and morbidity, the objectives of all valve research and development, has been to increase the functional life span of the bioprosthesis so that it can be put into patients only once, and will last the life of the patient. This has thus far been an extremely difficult goal to reach.
There may be another option, however, for the use of tissue heart valves in the younger population. Rather than building valves that last longer, it may be more appropriate to build valves that can be routinely replaced in a way that induces negligible patient morbidity. The objectives would therefore be not to have extremely durable valves, but rather valves that can be easily removed when they begin to fail and new ones inserted. The technologies that make this possible already exist with the advances made in the field of catheter-based endovascular procedures, and the more broad field of Minimally Invasive Surgery (MIS).
The field of MIS is growing at an accelerating pace. The approach involves the use of small surgical probes, cannulas, video cameras and remote staplers and suture drivers that enable surgery to be done without requiring large incisions. Most MIS is done with several small incisions, simply to allow the passage of these instruments into the patients body. The principal advantages of MIS is that the patient is subjected to less surgical trauma and has a dramatically reduced hospital stay, which in turn significantly reduces the operating costs of the clinical center. Current generation minimally invasive procedures are being carried out using endoscopes and long-reaching surgical tools. Typically, the patient""s abdomen is inflated with carbon dioxide and the instruments are inserted through small incisions. The surgeons then perform the procedures using endoscopic visualization. For cardiothoracic surgery, similar small incisions are created between the ribs and the heart is placed on bypass using multiple cannulas with balloons that can selectively shut off blood flow through the heart, and direct it through oxygenators.
Other technologies are being developed to do surgery on beating hearts, as to completely avoid placing the heart on bypass. Many of these procedures involve the use of specialized catheters that deploy devices or tools that perform a wide range of procedures on the beating heart. Typical beating heart procedures are endovascular balloon dilatation of arteries and stent placement. Deployment of stents and other permanent devices has become commonplace, but to date, no successful, catheter deployable valve has been developed.
While U.S. Pat. No. 5,545,214 discloses a balloon-deployable tissue valve, the technology is similar to that of stents, and is not ideal for tissue heart valves. The material that anchors the valve in the patient=s aortic root is permanently deformed through the bending of metal components, and is not intended to be re-collapsed into its original configuration. Practically the same approach is disclosed in U.S. Pat. No. 5,411,552. U.S. Pat. No. 5,554,185 discloses a means of deploying the valve by inflating of a hollow valve frame with a liquid that hardens. U.S. Pat. No. 5,545,209 describes the use of balloon technology to permanently distend and deploy an endoprosthesis, typically a vascular segment for treating abdominal aneurysm. This patent makes reference to xe2x80x9ca tubular prosthesis disposed on said catheter over at least a portion of said balloon.xe2x80x9d The major concepts disclosed by all of these patents are similar: the permanent deployment of a bioprosthetic heart valve. A permanently deployed tissue heart valve, whether it is done using MIS technology or not, is subject to the same requirements as conventional tissue valves: it must be very durable. Good durability, however, is not easily attained. The manufacturing process of tissue heart valves is very mature and complex from the quality control point of view, and only minimal improvements in valve durability have been achieved in recent years. Major improvements in valve durability are therefore not expected in the near future.
The present invention addresses the drawbacks discussed above, as well as other problems encountered with the prior art, to provide a system for minimally invasive removal and re-insertion of a bioprosthetic heart valve. One key feature of the present invention is a valve that can be collapsed after many years of use in the patient. The collapsing or expanding process does not involve any permanent deformation of components, as has been required for the systems disclosed in the preceding patents. A properly collapsible valve is first removed from the patient using catheters, when it has failed to provide proper function to the patient, a new version of the same temporary collapsible valve is inserted using the same catheter technology.
According to the present invention there is provided a system for minimally invasive removal and re-insertion of a bioprosthetic heart valve. Broadly stated, the device is sufficiently collapsible so as to be able to pass through the lumen of a catheter inserted into the femoral artery, or other large vessel. The collapsed valve is re-expanded when in place in order to fit into a permanent housing in the patients heart and assumes a fully functioning state. Integral to this system of removal and replacement of a prosthetic heart valve is an expandable xe2x80x9coperative platformxe2x80x9d that is deployed near the site of the valve so that it stabilizes the catheters and other instruments during the valve removal and reinsertion process.
In accordance with a first aspect of the present invention, there is provided a two component valve system comprised of a permanent housing which remains in the patient, and a collapsible valve which is replaced when it becomes necessary.
In accordance with a further aspect of the present invention, there is provided a permanent housing with an integrated sewing ring which is affixed to the patient aorta or other tissue by means of sutures or staples.
In accordance with another aspect of the present invention, there is provided a collapsible inner frame onto which several leaflets or flexible occluders are affixed, comprised of several articulating or hinged components which have a substantially smaller perimeter when fully collapsed, than when fully expanded.
In accordance with still another aspect of the present invention, there is provided an inflatable or distensible xe2x80x9csurgical platformxe2x80x9d which can be delivered to a site near the heart in a collapsed state and distended at that site such that it anchors the numerous catheters and devices in space thereby ensuring proper controlled manipulation of their distal ends, when acted upon by controls at their proximal ends.
In accordance with still another aspect of the present invention, there is provided an integrated check valve within the surgical platform that enables controlled ejection of blood from the ventricle during the process of collapsible valve removal and replacement.
In accordance with yet another aspect of the present invention, there is provided a split wall or xe2x80x9cmonorailxe2x80x9d catheter system which can guide larger instruments and devices between the outside of the patient and the surgical platform during the course of a valve replacement procedure.
In accordance with yet another aspect of the present invention, there is provided a tracking and visualization system that can generate accurate images or graphical representation of the catheters and other components on a computer screen so as to accurately represent the position of the real components inside the body of the patient.
Although the prosthetic collapsible valve of the present invention may incorporate various number of leaflets, a preferred embodiment of the valve incorporates three (3) valve leaflets.
Although the collapsible valve of the present invention may incorporate a wide range of leaflet materials, such as synthetic leaflets or those constructed from animal tissues, a preferred embodiment of the valve incorporates three (3) valve leaflets constructed from sheets of chemically preserved bovine pericardium.
Although the permanent outer frame of the prosthetic cardiac valve of the present invention may be constructed from a wide range of materials including metals and plastics, a preferred embodiment of the outer frame is constructed from stiff, rigid metal such as stainless steel.
Although the collapsing mechanism of the collapsible valve of the present invention may incorporate various means of remaining permanently expanded within the permanent outer frame, a preferred embodiment of maintaining the collapsible valve in its expanded state is by means of precision machining of the components of the inner frame so that a xe2x80x9csnappingxe2x80x9d action holds them in their expanded position by means of an interference fit between components.
Although the collapsible valve of the present invention may be collapsed by various means, a preferred embodiment of the valve collapsing means incorporates one or more projections or xe2x80x9chandlesxe2x80x9d that protrude from the collapsible frame so that they can be grabbed by a catheter-based snare means.
Although the collapsible valve of the present invention may be expanded by various means, a preferred embodiment of the valve expanding means incorporates an articulating expanding means that does not require the use of balloon technology to expand the collapsible frame.
Although the system for minimally invasive insertion of a collapsible valve may make use of numerous means of stabilizing the proximal ends of the catheters, a preferred embodiment of the procedure is the use of a stabilizing surgical platform that can be anchored distal to the aortic valve. The surgical platform incorporates slots and fixtures for attaching and holding catheters in slots that stabilize the movement and position of the distal ends of the catheters so that deflection and manipulation of the catheter ends is done in a controlled way.
Although the system for minimally invasive insertion of a collapsible valve may make use of numerous means of temporarily augmenting the action of the contracting heart by means of valves, a preferred embodiment of the procedure is the incorporation of an integrated check valve within the surgical platform that becomes functional once the platform is expanded in place. The integrated check valve can be fabricated out of polymer and have one or more occluding leaflets. The leaflets are soft and pliable and enable the passage of catheters and other devices past and through the leaflets.
Although the system for minimally invasive insertion of a collapsible valve may make use of numerous catheters to deliver the components of the collapsible valve system into the desired site, a preferred embodiment of the procedure is the use of a xe2x80x9cmonorailxe2x80x9d or slotted catheter sheath that enables larger devices to be guided along the outside of the slotted catheter sheath to the operative site.
Although the system for minimally invasive insertion of a collapsible valve may make use of numerous imaging or visualization techniques, a preferred embodiment of the procedure is the use of a ultrasonic or electromagnetic sensors affixed to the catheters and components such that their position can be detected and tracked in 3-D space, in sufficient spatial and temporal resolution and precision, so as to make the procedure easy and accurate.
As can be seen by those skilled in the art, an advantage of the present invention is the provision of a valve system that allows for safe and convenient removal and replacement of a collapsible valve when it begins to fail.
Another advantage of the present invention is the provision of an expandable, re-collapsible tissue-based heart valve.
Yet another advantage of the present invention is the provision of a catheter-based valve delivery system.
Still another advantage of the present invention is the provision of a stable surgical platform within which catheter-based manipulators can be securely anchored so that intracardiac procedures can be properly executed.
Another advantage of the present invention is the provision of a synthetic valve integrated with the surgical platform to act as a temporary check-valve while the expandable, re-collapsible tissue-based heart valve is being replaced.
Yet another advantage of the present invention is the provision of a slotted catheter sheath that can act as a xe2x80x9cmonorailxe2x80x9d guide to shuttle components along the outside of the sheath between the exit/entry port of the patient and the surgical platform within the heart.
Yet another advantage of the present invention is the provision of a ultrasound or electromagnetic catheter guidance system that can track the position and motion of the catheters and devices during the procedure and display images of the system components on a video display monitor, so as to make the procedure easy and accurate.
Still other advantages of the invention will become apparent to those skilled in the art upon a reading and understanding of the following detailed description, and accompanying drawings.